외반부하증후군(Valgus overload syndrome)

1. Elbow joint

Many acute and chronic injuries occur as a result of throwing. 

During the throwing motion in the phase of late cocking to acceleration, there are tremendous valgus forces that are pulling the elbow.

The valgus overload results in enormous tension on the medial side trying to pull things apart (yellow arrows), while the lateral side will be under compression (blue arrows). On the posterior side it causes shear forces along the head of the olecranon (black arrow).

2. Valgus overload syndrome

The tension on the medial side causes a tear of the ulnar collateral ligament. 

Compression on the lateral side causes an osteochondral lesion of the capitellum. 

The shear forces on the posterior side cause arthrosis.

3. Tommy John Surgery